Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with graphical user interface showing our new design.

The dash-dash broken lines around the FIGURE show a display screen or portion thereof and form no part of the claimed design. The dash-dash and dot-dot broken lines within the FIGURE show certain text and graphics that from no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 